1. Field of the Invention
The present invention relates to a deposition method, and more particularly, to a method of physical vapor deposition with substantially good step coverage on the bottom and the sidewall in the contact holes.
2. Description of the Prior Art
Physical vapor deposition (PVD) is one of deposition methods frequently used in the modern semiconductor industry. For example, the barrier layers containing Ti, TiN, or TiW, the Al plug, and the interconnection are all formed by the PVD technique.
As the lateral feature size of the semiconductor devices continuously decreases to sub-micron range while the dielectric thickness remains the same, the aspect ratio of contact holes is thus increased, and the step coverage issue for the contact hole becomes a bottleneck as shown in FIG. 1B. FIG. 1A shows a configuration of the conventional PVD process, where the substrate 120 is supported by a chuck 140, and the direction of the deposition from the target 100 is always vertical to the surface of the substrate 120. This conventional PVD method has a limit to its poor step coverage.
An alternative method called ionized metal plasma (IMP) is developed for improving bottom step coverage. Unfortunately, the sidewall step coverage of the IMP has not been improved, and is possibly even worse than the conventional PVD method. The step coverage issue is crucial to modern semiconductor devices and becomes important to some specific processes. For instance, the step coverage of the barrier layer on the contact sidewall is significant for the copper metallization process, in which the barrier layer is mainly used to prevent copper from diffusing into the substrate. Moreover, the step coverage of the copper seed layer is also important for the copper metallization process, in which a too thin seed layer will form unwanted voids after filling in the copper.
According to the foregoing reasons, there is a need for a method of physical vapor deposition with substantially good step coverage on the bottom and the sidewall in the contact holes.